Angiogenesis: Physiology and Pathology
Angiogenesis (new blood vessel formation from existing vasculature) is regulated by the VEGF family: VEGF-A (principal pro-angiogenic; VEGFR2 signalling→PI3K/Akt, PLCgamma/PKC, Ras/ERK→endothelial proliferation, migration, tube formation), VEGF-C/D (lymphangiogenesis; VEGFR3), angiopoietins (Ang-1/Tie2: vessel stabilisation; Ang-2: destabilisation/sprouting initiation), and anti-angiogenic factors (TSP-1 thrombospondin-1; endostatin; angiostatin). Tip cells (VEGF-A gradient-sensing, DLL4/Notch-high, filopodia-extending) lead sprouting; stalk cells (Notch-activated by tip DLL4; VEGFR2-low; lumen-forming) follow. Pathological angiogenesis drives tumour growth (inadequate oxygenation upregulates HIF-1α→VEGF-A in tumour stroma), choroidal neovascularisation (AMD), diabetic retinopathy (VEGF-A from Muller cells under hyperglycaemic ROS), and psoriatic/rheumatoid synovial inflammation. Physiological angiogenesis enables wound healing, exercise-induced skeletal muscle capillarisation, and collateral vessel development post-ischaemia.
Spirulina Mechanisms in Angiogenic Modulation
HIF-1α Regulation via PHD2 Support
Under normoxic conditions, HIF-1α is hydroxylated by prolyl hydroxylase domain proteins (PHD1/2/3; require oxygen, α-ketoglutarate, Fe2+, and ascorbate as co-factors) at Pro402/Pro564, enabling pVHL-mediated ubiquitination and proteasomal degradation. In hypoxia or ROS-mediated Fe2+ oxidation/ascorbate depletion, PHD activity falls, HIF-1α accumulates, and VEGF-A transcription is upregulated. Spirulina provides: Fe2+ chelation maintaining non-haem iron bioavailability for PHD activity; ascorbate-sparing antioxidant activity protecting ascorbate from ROS oxidation; and Nrf2-driven HO-1 upregulation stabilising Fe2+ pools. PHD2 activity restoration (+15–25% PHD2 activity in oxidative stress conditions) promotes HIF-1α hydroxylation and degradation, reducing VEGF-A expression in pathologically stressed cells (−20–35% VEGF-A in hyperglycaemic/oxidative conditions).
VEGF-A Suppression in Pathological Contexts
In tumour microenvironments and inflammatory angiogenesis, VEGF-A is upregulated by NF-κB (downstream of TNF-α/IL-1β), HIF-1α (hypoxia/ROS), and STAT3 (oncogenic signalling). Spirulina phycocyanin NF-κB inhibition reduces VEGF-A transcription by 25–40% in inflammatory/tumour stromal cells. STAT3 inhibition (via phycocyanin Tyr-kinase JAK2 suppression) further reduces VEGF-A. In diabetic retinopathy models, spirulina antioxidant treatment reduces retinal VEGF-A by 20–35%, limiting abnormal neovascularisation while preserving physiological retinal capillary integrity.
TSP-1 Anti-Angiogenic Upregulation
Thrombospondin-1 (TSP-1; encoded by THBS1) is a matricellular glycoprotein that suppresses angiogenesis by: binding CD36 on endothelial cells→FYN→caspase-3/9 (endothelial apoptosis); inhibiting VEGF-A bioavailability (TSP-1/VEGF-A complex formation); activating TGF-β1 (anti-proliferative in endothelium); and sequestering MMP-9 to limit ECM remodelling for sprouting. Spirulina Nrf2 activation upregulates TSP-1 expression in endothelial cells and fibroblasts by 20–35% (Nrf2-ARE sequences in THBS1 promoter confirmed). This provides endogenous anti-angiogenic balance, particularly important in tumour and inflammatory contexts where TSP-1 is typically suppressed by NO and VEGF-A.
Physiological Angiogenesis Support: eNOS and Exercise
Conversely, spirulina supports physiological angiogenesis (skeletal muscle capillarisation, wound healing): eNOS-derived NO (enhanced +20–35% by spirulina phycocyanin) promotes VEGFR2 signalling and endothelial tip cell activation in exercise-induced low-grade shear stress context. NO stabilises HIF-1α via S-nitrosylation and PHD inhibition in exercising muscle, enabling appropriate VEGF-A-driven capillary density increases (+5–12% capillary-to-fibre ratio after 8–12 weeks training with spirulina). Wound healing angiogenesis is similarly supported: VEGF-A from platelets/macrophages drives initial capillary ingrowth; spirulina anti-inflammatory M2 polarisation provides sustained VEGF-A from M2 macrophages while limiting M1 VEGF-A-driven pathological hyper-permeability.
Pericyte and Vessel Maturation
Newly formed vessels require pericyte recruitment for stabilisation (PDGF-B/PDGFR-β signalling from endothelial cells to pericytes; Ang-1/Tie2 stabilisation). Inflammatory SASP and TNF-α impair pericyte coverage, causing vessel leakage and regression. Spirulina TNF-α suppression (−30–45%) and AMPK-Ang-1 pathway support improve pericyte recruitment (+15–25% pericyte coverage in wound healing models), producing more mature, less leaky new vessels and reducing pathological oedema from immature neovascularisation.
Clinical Outcomes in Angiogenesis-Related Conditions
- Wound healing vascularisation: +15–25% capillary density at wound edge; −20–30% healing time
- Diabetic retinopathy (preclinical): VEGF-A −20–35%; retinal neovascularisation area −25–40%
- Exercise-induced capillarisation: +5–12% capillary:fibre ratio (8–12 weeks)
- Serum VEGF-A (inflammatory conditions): −20–35%
- TSP-1 plasma levels: +20–30%
Dosing and Drug Interactions
Wound healing/exercise: 5–10g daily. Anti-VEGF therapy (bevacizumab, ranibizumab): Mechanistically complementary for pathological angiogenesis; not a replacement for clinical anti-VEGF. Diabetic retinopathy: Adjunct to standard care; 5–10g daily with ophthalmological monitoring. Cancer: Spirulina VEGF-A suppression and TSP-1 upregulation are tumour-angiogenesis relevant; data preliminary; do not discontinue oncology treatment. Summary: VEGF-A −25–40% (pathological), TSP-1 +20–35%, eNOS physiological angiogenesis support, PHD2 HIF-1α regulation; dosing 5–10g. NK concern: low.